1. Field of the Invention
The present invention is related to the production of gaseous olefins, and most particularly to the production of propylene and butylene from petroleum hydrocarbons by catalytic conversion in which solid, acidic catalysts are used.
2. Discussion of Related Art
Ethylene, propylene, and butylene are produced conventionally from petroleum hydrocarbons, such as natural gas, naphtha or light gas oil by well known tubular furnance pyrolysis. They are also produced from heavy petroleum fractions by pyrolysis over heat carrier or by catalytic coversion of lower aliphatic alcohol. In modern refineries, gasoline and light gas oil are produced by conventional catalytic cracking, together with gaseous olefines as by-products at a yield of only less than 15 percent by weight of the feedstocks.
Recently, investigations for catalysts which are more effective for converting petroleum hydrocarbons to gaseous olefins have made and the results of the investigations have been reported in various patents. U.S. Pat. No. 3,541,179 discloses fluidized catalytic cracking process for producing gaseous olefins. The catalysts include copper, manganese, chromium, vanadium, zinc, silver, cadimum or their mixtures which are deposited on alumina or silica. U.S. Pat. No. 3,647,682 discloses the preparation of lower olefins from butane or middle distillate by catalytic cracking over a Y type zeolitic molecular seive. More recent patents in the same area include DD No. 152, 356 which describes a method for producing C.sub.2 to C.sub.4 olefins from gasoline or vacuum gas oil by a fixed or moving bed catalytic cracking over amorphous silica-alumina catalysts at a temperature of 600.degree. to 800.degree. C. and a contact time of for 0.3 to 0.7 seconds, with yields of 13.5% for ethylene, 6.3% for propylene and 10.5% for butylene. JP No. 60-222,428 discloses a process using the well known zeolite ZSM-5 as a catalyst and C.sub.5 to C.sub.25 paraffinic hydrocarbons as feed stock. The process is carried out at a reaction temperature of 600.degree. to 750.degree. C. and a space velocity of 20 to 300 per hour, with 30 percent yield for C.sub.2 to C.sub.4 olefins. When naphtha is used, the yields of ethylene, propylene, and butylene are 16, 14, and 1.8 percent, respectively. These above processes involve high cracking temperature, stringent requirement for material of cracking apparatus, and hydrocarbon feeds which are limited by a relatively narrow boiling ranges. The objectives of most of these processes aim are to obtain a higher production of ethylene.